In the last few years, there has been a trend in microscope systems which clearly goes in a direction of complex systems wherein the microscope defines an essential component but is to be considered in the context of an overall solution which is mostly computer supported. Increasingly, control and image data evaluation takes place automatically via computers. This effects, for example, the area of automatic scanning systems for primary screening for pathology/cytology or pharmaceutical molecular biology. In addition, a trend toward miniaturization of all components is present. A very essential microscope component is a flexible, compact and reliable illumination.
Classical light sources for microscopes, such as halogen lamps, have disadvantages with respect to these requirements. They are expensive, require high electric power, have a high thermal emission, a short service life and their color spectrum changes with changing brightness. In addition, the constructional configuration and weight are comparatively high.
U.S. Pat. No. 4,852,985 discloses an illuminating device for the flexible configuration of illuminating structures usual for microscopes. Here, semiconductor light sources such as two-dimensionally arranged LEDs are used as light sources. The realization of the different illuminating structures takes place via targeted switch-on of the required LEDs. In addition, a device for adjusting brightness can be present. The different illuminating types in a microscope are realizable without additional optical components because of this targeted switch-on of a number of LEDs. The surface light source can also be configured via the two-dimensional arrangement of LEDs which emit different colors such as red, green and blue (RGB). The arrangement of the individual colors on the array is of great significance in order to generate a color impression as uniformly as possible without color fringes in the object plane. For this purpose, U.S. Pat. No. 4,852,985 discloses a variation for a defined arrangement of LEDs for a three-color array. A ground glass screen is required in this solution to prevent illumination nonuniformity. The ground glass screen is mounted ahead of the surface light source.
An LED light standard for photo microscopy and video microscopy is described in U.S. Pat. No. 5,489,771. In this calibration system, the intensity of a compact LED light source is controlled with the aid of a detector. A diffuser is mounted ahead of the LED light source and, in addition to ensuring a high light homogeneity, the diffuser ensures that a portion of the light radiation incidents on the laterally mounted detector and can be evaluated. In this standard light source, which is usable for calibration, the generated light intensities can be very precisely adjusted in that the energy, which is supplied to the LEDs, can be continuously compared to the detector via the control current loop. Preferably, the compact LED light source comprises LEDs which radiate in different colors (RGG or RGB) and can be individually driven. A single color light can be generated via the targeted driving of the LEDs and the use of bandpass filters. In the generation of pulse modulated light, it is necessary that the camera and/or video camera be correspondingly synchronized.
In DE 199 19 096 A1 (U.S. Pat. No. 6,795,239), a transmitted light illuminating unit for microscopes is described wherein a transparent microscope table is illuminated from below. The illuminating unit comprises one or several LEDs and is so configured that it can be mounted in the aperture diaphragm plane as well as ahead of a Köhler illuminating optic. A suitable scattering means is mounted ahead of the LEDs to ensure an illumination as uniform as possible. A disadvantage of this solution is that, when using only a few LEDs, an insufficient brightness can be made available for some illuminating methods (for example, the phase contrast method). The intensity made available is still further reduced by the use of additional scattering means.
DE 298 16 055 U1 likewise describes a microscope having an illuminating arrangement which is pivotally mounted. The illuminating arrangement is built up of discrete LEDs. With the suggested solution, it is true that with differentiated driving of the LEDs, structured illuminations can be realized such as for bright field, dark field, inclined and annularly-shaped illumination or phase contrast illumination; however, in this context, it is disadvantageous that emission can occur only in discrete wavelengths, as a rule, red, green and blue. A white light illumination with full daylight spectrum, which is relevant for most microscope applications, or other desired emission spectrums cannot be generated with this solution.
The illuminating arrangement described in U.S. Pat. No. 6,373,568 comprises a plurality of individual LEDs which realize different discrete wavelengths. The disadvantage of this solution is the very costly and complicated configuration. In addition, no continuous spectrum can be generated with the described illuminating arrangement.
While with the conventional lamps, which had been used so far as excitation light sources for the fluorescence microscopy, a short service life as well as a high initial cost and maintenance cost were to be expected, the problem in the use of LED illumination as excitation light sources is present that LEDs having an adequate light density are available not for all wavelengths or are very cost intensive. These conventional lamps can be, for example, arc lamps or halogen lamps.